1. Field of the Invention
The present invention relates to a data line driving circuit, a driver IC including the data line driving circuit, and a display apparatus operated by the driver IC.
2. Description of Related Art
A flat panel display, such as a liquid crystal display apparatus, an organic EL (Electro Luminescence) display and the like has become popular. The liquid crystal display apparatus is used for a display apparatus in various fields, such as a display apparatus of a television set, a display apparatus of a personal computer, a displaying apparatus of a digital camera, and a display apparatus of a cellular phone and the like. Also, the organic EL display is considered to be a promising apparatus as a next generation display apparatus and used in the displaying apparatus of the cellular phone and the display mounted in a car, and the like. The flat panel display includes a driver IC. The driver IC is used as a circuit which drives a displaying element and controls displaying a picture.
The flat panel display typically includes a displaying region, which includes a plurality of pixels arranged in a matrix shape. The driver IC controls light from the respective pixels to execute displaying a picture on the displaying region. Each pixel includes a displaying element such as a liquid crystal material, an organic EL element or the like. Each displaying element is controlled by a signal from the driver IC.
For example, in the display apparatus of the personal computer, a picture signal supplied from a main body of the personal computer is received by a controller LSI mounted in the display apparatus. The controller LSI supplies a digital signal corresponding to the picture signal to the driver IC. The driver IC generates an analog signal based on the obtained digital signal and outputs it to the respective pixels arrayed in the matrix shape. In accordance with this, the displaying element of each pixel is controlled, and the picture is displayed inside the displaying region.
Typically, the number of outputs (hereinafter referred to as output number) of the driver IC is fixed. Thus, in a case that the number of pixel columns (the number of dot columns) is not equal to the integral multiple of the output number of the driver IC, a countermeasure is conventionally employed in which several kinds of the driver ICs whose output numbers differ from each other are used at the same time. However, when the several kinds of the driver ICs whose output numbers differ from each other are used at the same time, electric properties such as driving performances of those driver ICs are different from each other. Hence, there is a case that variation in display quality occurs between the different driver ICs. In order to suppress a drop of the display quality, a technique is disclosed which can change the output number of the driver IC in Japanese Laid-Open Patent Application JP-P2005-215007A.
FIG. 1 is a block diagram showing source driver ICs 120 and their output wirings disclosed in JP-P2005-215007A. In FIG. 1, a region (displaying region 301) surrounded with a dash line is provided with a plurality of pixels and serves as a displaying region in which a picture is displayed. In the technique disclosed in JP-P2005-215007A, the displaying region 301 is used for displaying a picture of 454 dots×RGB (=1362 pixel columns). Specifically, an example is shown in which the output number of a central source driver IC 120b is 402 and each of the output numbers of the other two source driver ICs 120a and 120c of both ends is 480 among the three source driver ICs 120a, 120b and 120c. In this case, the total output number is 1362 (480+402+480).
As shown in FIG. 1, each of the source driver ICs 120a to 120c includes an output number control terminal 311, in addition to a plurality of display signal output terminals 310. Control signals (TEST1, TEST1B) 350 from a control circuit 105 (not shown) are supplied to the output number control terminals 311, respectively. In this example, the control signals (TEST1, TEST1B) 350 serving as the inputs to the respective output number control terminals 311 are kept constant, and the output numbers are kept constant. For example, when the control signals (TEST1, TEST1B) 350 of an L-level are supplied to the central source driver IC 120b, the output number can be set to 402, and when the control signals (TEST1, TEST1B) 350 of an H-level are supplied to the source driver ICs 120a and 120c of both ends, the output numbers can be set to 480.
In this way, the respective source driver ICs 120a, 120b and 120c switch between the 480 outputs and the 402 outputs, based on the control signals (TEST1, TEST1B) 350 supplied to the output number control terminals 311.
We have now discovered following facts. JP-P2005-215007A does not describe a specific configuration used for switching the output numbers of the driver ICs. In addition, these driver ICs cannot stop electric current, which becomes unnecessary, flowing into outputs when the output numbers are switched. Cutting the unnecessary electric current flowing into the outputs leads to a reduction in electric current consumption. Thus, this is one of the important electric properties that are always required for the driver IC.